1. Field of the Invention
The invention relates to a machine for producing a fibrous material web, in particular a tissue paper or bathroom tissue web, with at least one pre-press embodied as a shoe press, a main press comprised of a press roll and a drying cylinder, an endless top belt guided through the nips of the pre-press and the main press, and an underfelt guided via a bottom roll of the pre-press, wherein the top belt supplies the fibrous material web that has been preformed in a former first to the pre-press and then to the main press. The invention also relates to the method of producing a fibrous material web by means of the machine.
Moreover, the invention also relates to a machine for producing a creped tissue paper web that is pressed onto a peripheral surface of a single tissue drying cylinder in a wet state and finish dried in contact with the surface and removed from the surface after drying by a creping doctor. The creped product can be, e.g., bathroom tissue, etc.
2. Discussion of Background Information
DE-A-42 24 730 (U.S. Pat. No. 5,393,384) has disclosed different embodiments of a bathroom tissue machine of the aforementioned type. One of these known embodiments includes a total of three press points, namely two pre-presses between two top rolls and two bottom shoe press rolls with a flexible roll jacket, as well as one main press with a press roll and a drying cylinder. The paper web is produced on a roll former between a drainage screen and a top belt. Bottom belts embodied as permeable felts are guided together with the paper web and the top belt through the two pre-presses.
According to another known embodiment, a top belt removes the paper web from a former in order to then guide it with an underfelt through a pre-press between a top roll and a bottom roll to a main press between a press roll and a drying cylinder. In another known embodiment, the press roll is a shoe press roll.
With the exception of the use of shoe presses, these known embodiments approximately correspond to two-felt tissue apparatuses that were once standard but are no longer used in the new bathroom tissue machines.
In these known two-felt tissue machines, the overfelt is very dense and the underfelt is very water-absorbent. To achieve as great a drainage as possible by means of the underfelt, the bottom roll is embodied as a suction roll.
The problem that occurs in a two-felt machine of this type which led to a rejection of this principle and instead to the current use of single felt machines is comprised of the fact that with increasing web travel speed, preparatory drainage cannot be carried out rapidly enough, even with a suction press and, as a result of an insufficient water drainage, the web is crushed in the pre-press.
For this reason, the use of a shoe press as the pre-press is actually advantageous in principle. However, in the embodiments disclosed in DE-A-42 24 730, it is among other things disadvantageous that the respective shoe press rolls are disposed in the bottom position since the paper web comes from the forming wire in a very wet state, i.e., with a dry matter content of approximately 6% to 8%.
The blind bores or grooves in the surface of the press jacket cannot absorb the entirety of the accumulating water due to their depth, which is limited for manufacture conditional reasons. This could be a reason for the fact that in most of the embodiments disclosed in DE-A-42 24 730, two pre-presses are provided and, in this instance, a suction press roll is additionally provided in the main press.
In most of the embodiments disclosed in DE-A-42 24 730, a waterproof or watertight top belt is additionally used.
In particular in comparison to a single felt machine, the known embodiments of the two-felt machine consequently take up a relatively large amount of space, particularly because in the instances mentioned, two pre-presses and a main press are provided, which main press does not remove any water on the creping cylinder.